The present invention relates to an optical network unit (ONU) which interconnects sources of telecommunications services with customer equipment at one or more customer premises. The present invention particulary relates to a card cage that supports circuit cards in installed positions in an ONU.
An ONU may contain a group of circuit cards including a common card and service cards that are electrically interconnected with the common card. Each service card has circuitry corresponding to a particular telecommunications service provided to customers served by the ONU. The common card and the service cards are installed in a card cage structure which includes a backplane. Specifically, the common card and the service cards are supported together on the backplane in installed positions perpendicular to the backplane. The backplane is configured with circuitry that defines the electrical interconnections between the common card and the service cards.
An individual circuit card can be electrically disconnected from the other circuit cards by removing it from its installed position on the backplane, and a substitute circuit card can be installed in its place on the backplane. However, the backplane is a relatively permanent fixture in the ONU. Therefore, the adaptability of the ONU to provide differing or newly developed telecommunications services is limited by the particular backplane circuitry in the ONU.
In accordance with a principal feature of the present invention, an apparatus includes circuit cards, a card cage, and electrical connector hardware. The card cage releaseably engages and supports the circuit cards in installed positions in the card cage. At least one pair of the circuit cards have serial interconnections with each other. The electrical connector hardware defines all of those serial interconnections and is free of a backplane.
In accordance with another principal feature of the invention, the circuit cards are accessible for electrical interconnection with each other, and electrical disconnection from each other, while remaining in their installed positions in the card cage. Side walls of the card cage engage and support the circuit cards orthogonally between the side walls. The side walls are configured to receive and guide movement of each circuit card between the side walls for installation and removal of the circuit cards from their installed positions separately from each other.
In accordance with yet another principal feature of the invention, the card cage has an end wall facing between the side walls. The end wall also engages the circuit cards and is free of backplane circuitry for defining serial interconnections between the circuit cards. In a preferred embodiment of the invention, the end wall functions as a heat sink to conduct heat from the circuit cards. The end wall in the preferred embodiment further provides the circuit cards with parallel electrical interconnections consisting of ground connections. This feature of the end wall is especially beneficial in the absence of backplane circuitry that might otherwise provide the circuit cards with ground connections.